1. Field of the Invention
This invention relates to refrigeration systems having internally compounded two-stage compressors having interstage cooling. More specifically, it relates to an oil return system for such a compressor, which has an oil separator associated therewith.
2. Description of the Prior Art
Low evaporator temperatures are encountered in many industrial refrigeration applications. In such applications it is often found that two-stage rather than single stage compression is advantages, either to achieve greater economy or to avoid excessive compression ratios and compressor discharge temperatures. In a typical two-stage reciprocating compressor system the discharge gas from the low pressure stage of the compressor is normally very highly superheated and is too hot for the suction of the high pressure stage of the compressor. An interstage cooling system sometimes referred to as a de-superheater, in commonly used to reduce the gas temperture so that the discharge from the high pressure stage of the compressor is not excessively high.
Lubricating oil is continuously carried into the high pressure stage discharge line along with high pressure, high temperature gaseous refrigerant. An oil separator is commonly installed after the high stage compressor to receive the oil and refrigerant mixture and separate the oil from the gas.
It is also common practice when using an integral two-stage compressor to maintain the crankcase at the intermediate stage pressure. Common design practice is also to return the oil from the oil separator to the crankcase.
With certain oil separator systems, particularly those having a minimal number of moving parts and adapted for use in transport refrigeration systems, the oil return discharge line to the crankcase may in some cases contain hot discharge gas. The hot discharge gas may, in some circumstances, raise the temperature and pressure of the crankcase to a level above the intermediate stage pressure. This condition is not desirable.